Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
Fuel cells can be categorized according to the type of electrolyte used, typically one of five types: proton exchange membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric-acid fuel cell (PAFC), solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC). Each of these types of fuel cell can use hydrogen and oxygen as the active materials of the fuel cell negative electrode (anode) and positive electrode (cathode), respectively. Hydrogen is oxidized at the negative electrode, and oxygen is reduced at the positive electrode. Ions pass through an electrically nonconductive, ion permeable separator and electrons pass through an external circuit to provide an electric current.
In some types of hydrogen fuel cells, hydrogen is formed from a hydrogen-containing fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell.
A fuel cell system can include a fuel cell battery, including one or more fuel cells (e.g., a fuel cell stack), and a fuel source, such as a fuel tank or a hydrogen generator. Hydrogen generators that supply hydrogen gas to a fuel cell can be an integral part of a fuel cell system, or they can be removably coupled to the fuel cell system. A removable hydrogen generator can be replaced with another one when the hydrogen producing reactants have been consumed. Removable hydrogen generators can be disposable (intended for only a one-time use). Both removable and permanently installed hydrogen generators can be refillable (intended for use multiple times) to replace consumed reactant materials.
Hydrogen generators can produce hydrogen using a variety of reactants and a variety of methods for initiating the hydrogen generating reactants. Hydrogen gas can be evolved when a hydrogen containing material reacts. Some hydrogen containing compounds can react with another reactant to produce hydrogen gas, when the reactants are mixed together, in the presence of a catalyst, heat or an acid, or a combination thereof. Some hydrogen containing compounds can be heated to evolve hydrogen in a thermochemical decomposition reaction.
In selecting reactants for use in a hydrogen generator, consideration may be given to the following: (a) stability during long periods of time when the hydrogen generator is not in use, (b) ease of initiation of a hydrogen generating reaction, (c) the amount of energy that must be provided to sustain the hydrogen generating reaction, (d) the maximum operating temperature of the hydrogen generating reaction, and (e) the total volume of hydrogen that can be produced per unit of volume and per unit of mass of the reactant(s).
An object of the present invention is to provide a packaged fuel unit containing a reactant that can produce hydrogen gas when heated. The packaged fuel unit desirably has one or more of the following characteristics: contains a maximum quantity of reactant to produce a maximum quantity of hydrogen gas and a minimum volume of packaging or other components; has a simple design and is easy and inexpensive to manufacture; reliably contains its contents before and after use; provides good heat transfer to the reactant therein; and has a package that facilitates selective heating of individual segregated quantities of reactant to provide hydrogen on an as-needed basis.
Another object of the invention is to provide a hydrogen generator using the fuel units to produce hydrogen gas safely and economically. The hydrogen generator desirably has one or more of the following characteristics: fuel units can be easily and safely replaced as the reactant therein is consumed; includes a holder containing a maximum number of expensive and reusable components; includes a heating system can be controlled to heat the reactant and provide hydrogen on an as-needed basis.
Yet another object of the invention is to provide a fuel cell system including a fuel cell battery and a hydrogen generator that can be safely, easily and economically operated.